Fix deletion of events (wrong date filter)

aleksis/apps/untis/util/mysql/importers/events.py

@@ -137,9 +137,8 @@ def import_events(
         ref[import_ref] = new_event
 
         # Delete all no longer existing events
-        for e in chronos_models.Event.objects.filter(
-            date_start__lte=validity_range.date_start,
-            date_end__gte=validity_range.date_end,
+        for e in chronos_models.Event.objects.within_dates(
+            validity_range.date_start, validity_range.date_end
         ):
             if e.import_ref_untis and e.import_ref_untis not in existing_events:
                 logger.info("Event {} deleted".format(e.id))